A tire condition monitoring apparatus is known as an apparatus that allows a driver to check the condition of the tires of a vehicle from the passenger compartment. The tire condition monitoring apparatus includes transmitters, which are respectively attached to wheel assemblies, and a receiver mounted on the vehicle. Each transmitter transmits transmission data including data indicating the condition of the tire to the receiver. The receiver receives the transmission data to acquire the condition of the tire.
In the tire condition monitoring apparatus described above, it is preferable that the receiver can identify the tire to which the tire condition included in the transmission data corresponds. In other words, it is preferable that the receiver can identify the wheel assembly to which the transmitter that has transmitted the received transmission data is attached. This type of tire condition monitoring apparatus is disclosed, for example, in Patent Document 1.
The tire condition monitoring apparatus disclosed in Patent Document 1 is mounted on a vehicle including rotation angle detecting devices that detect the rotation angles of the wheel assemblies. When detecting that the rotation angle of the wheel assembly matches a predetermined specific angle, the transmitter transmits transmission data. The receiver obtains the rotation angle of each wheel assembly from the rotation angle detecting device upon reception of the transmission date. The receiver identifies the wheel assembly to which each of the transmitters is attached based on the variation of the rotation angle of each wheel assembly obtained upon reception of the transmission data.
Some vehicles have a null point, at which signals of transmission data transmitted from the transmitters interfere with each other. When the specific angle at which the transmission data is transmitted coincides with the null point, the receiver cannot receive the transmission data transmitted at the specific angle. As a result, the receiver may be unable to identify the wheel assembly to which each transmitter is attached. Therefore, in some cases, two or more specific angles, at which transmission data is transmitted, are set.
When two or more specific angles are set, the rotation angles obtained upon reception of transmission data are classified for each specific angle at which the transmission data is transmitted, and the variation is obtained for each classified rotation angle.